Character generator for radar display

ABSTRACT

A character-generating system for use with a radar system wherein coded radial element signals and coded circular element signals are generated in response to the trigger and heading signals, respectively, generated by the radar system. The coded radial and circular element signals are combined to form a plurality of pattern signals representing a plurality of characters. The pattern signals are then selected and combined with the video radar information to form a composite signal which is fed to the radar display.

Unite 343/5El 340/324.1X

CHARACTER TIONINC MEANSI References Cited UNITED STATES PATENTS 5/1965Dutton et al. 3,444,319 5/1969 Artzt et OUTPUT CONTlROLLER I6.

AND CIRCUITS TIME MONITOR E EMORY Primary Examiner-Rodney D. Bennett, Jr

Assistant ExaminerMalclm F. Hubler Attorney-Flynn & Frishauf ABSTRACT: Acharacter-generating system for use with a radar system wherein codedradial element signals and coded circular element signals are generatedin response to the trigger and heading signals, respectively, generatedby the radar system. The coded radial and circular element signals arecombined to form a plurality of pattern signals representing a pluralityof characters. The pattern signals are then selected and combined withthe video radar information to form a composite signal which is fed tothe radar display.

PATTERN SIGNAL SELECTOR TIME SIGNAL GENERATOR13 GATE CIRCUITS 29AUTOMATIC PATTERN SIGNAL I2 SELECTOR SIEGNENT COIEPii 343/5, 5 315/22(orig) G0ls 7/12, GO 1 s 7/22 RESET SIGNAL CIRCULAR ELEMENT SIGNAL SCOMPOSITE SICNAL Sv RADAR VIDEO SIGNAL GATE CIRCULARIB) OSCILLATORCIRCULARIT) (El); 340/324.l

RADARH) INDICATOR IIIXER10- Toshio Kaooka', Keisuke Suzuki; YoshiakiUeda; Naoyoshi ()ishi, Tokyo, Japan 824,514

Japan Radio Company, Limited Tokyo, Japan Takao Tsumura;

May 14, 1969 Japan TRIGGER SIGNALSJ LS NEADING SIGNAL (2) CIRCUIT Lii Hiii'l RADIAL DELAY Inventors App1.No.

Filed Patented May 18, 1971 Assignee 19 Claims, 9 Drawing Figs.

SIGNAL ENCODER RADIAL ELEMENT [32] Priority May 15,1968

[54] CHARACTER GENERATOR FOR RADAR DISPLAY FieldofSearch........

Patented May 18, 1971 V 3,579,234

7 Sheets-Sheet 5 S S S SIGNAL If OUTPUT 0F RADIAL DELAY cmcun 2 "l l bOUTPUT 0F F1 I RADIAL GATE 3 (c) OUTPUT WAVEFORM 0F .flIlIt-fl flflItL(d) RADIAL oscumom HEADING SlGNAL Sh u u FIG. 3

'OIO m m WQQWW Patented May 18,1971 3,579,234

7 Sheets-Sheet 4 Q-IO- I UIO'DIQLO Patented May 18, 1971 V 7 3,519,234

7 Sheets-Sheet 5 CIRCULAR m v ADIAL sLEMENT m h/ELEMENT SIGNAL 4 i SGMLENCODER ENOODER [51 (E ID (a) w) (E) MIXER/\I 1 (an) (em mosmc PATTERNSEGMENT mm DIGITTHREEB) COMPOSER CHARACTER GENERATOR FOR RADAR DISPLAYThe present invention relates to the generation of characters and thedisplaying thereof with radar video signals on the PPI indicator of aradar receiver or the like. More particularly, it relates to anapparatus for simultaneously representing alphanumeric charactersgenerated by utilizing the sweeping trigger and heading signals of aradar receiver, at a particular location on the PPI display of a radarreceiver of the like.

Radar receivers have, in the past, displayed only the echo signalsreceived from an object without displaying a reference image, such as atime reference signal giving the actual time when the echo signals arereceived by the receiver. This limitation has reduced the value of arecorder radar display when it is later reproduced because the displaypresents no time or any other reference data. Thus, it is difficult toidentify the display when it is reproduced at a later date.

In order to obviate this disadvantage, prior art radar displays havebeen recorded with voice signals carrying the necessary identificationinformation. But this practice does not provide a precise time referencewhich can change every second in synchronism with the reproduced radardisplay. Moreover, the construction and operation of such prior artdevices was quite complex due to the insertion of the voice signals.

Therefore, it is an object of the present invention to provide a devicefor simultaneously displaying radar signals and the necessary referencecharacters, such as an actual time reference.

It is a further object of the present invention to provide a radardevice for displaying reference characters which are separately arrangedin relation to one another, the characters being simultaneouslydisplayed with the radar signals on a PPI display at predeterminedpositions.

SUMMARY OF THE PRESENT INVENTION The character generator of the presentinvention receives the trigger and heading signals generated by a radarequipment. The sweeping trigger signal is delayed and is applied to, andstarts, a radial oscillator, the output of which is encoded into theradial element signals corresponding to the vertical components of thecharacters to be represented on the radar display.

The heading signal is delayed and is applied to, and starts, a circularoscillator, the output of which is encoded into circular element signalscorresponding to the horizontal components of the characters to berepresented on the radar display.

The radial and circular element signals obtained are applied to a mixerto produce coded segment signals corresponding to specific segments ofthe characters. These coded segment signals are then applied to asegment signal composer, wherein they are composed into a patter signalcorresponding to a specific character.

Further provided is an output controller for combining the signalscorresponding to the character to be displayed with the current radarsignals is synchronization with each other. The resultant compositeoutput signals of the output controller are fed to the, radar indicatorfor simultaneous representation on the PPI display thereof.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIG. 1 is a schematic block diagram of the component units of thepresent invention;

FIG. 2 shows the system of FIG. 1 in more detail;

FIG. 3 is a diagram illustrating the pulse waveforms used in theapparatus of this invention;

FIGS. 4 and 5 are diagrams illustrating the waveforms of the radial andcircular element signals, respectively, corresponding to the verticaland horizontal segments of reference alphanumeric characters;

FIG. 6 illustrates how the vertical and horizontal segment signals recombined into the signals representative of a specific alphanumericcharacter;

FlG. 7 illustrates the manner in which the waveforms of the vertical andhorizontal segment signals re automatically selected by the automaticpattern signal selector under control of the clock signals;

FIG. 8 illustrates how the selected vertical and horizontal segmentsignals are designated to their locations on a PPI display for theirrepresentation as an alphanumeric character; and

FIG. 9 id a diagram illustrating an example of the alphanumericcharacters represented on a PPI radar display to denote 23 o'clock-57minutes-08 seconds, the l6th of Oct. in 1968.

The invention will be described hereinbelow with reference to generatingalphanumeric characters. However, it should be clear that the inventiveconcept disclosed is equally applicable to the generation of other typesof characters or reference information.

FIG. 1 illustrates a general block diagram of the invention. Theapparatus of this invention, generally indicated by the elementsincluded within the dashed block 100, is connected to a radar indicatorof conventional construction, generally indicated by block I. The radarindicator 1 generates sweep trigger and heading signals in a manner wellknown in the art.

A radial signal encoder channel 101, including a radial delay circuit 2,a radial gate circuit 3, and a radial oscillator 4 (of standardconstruction) and a radial element signal encoder 5, all coupledtogether in series, is connected to the trigger signal output of theradar indicator 1 to receive the sweep trigger signals 5,. A reset lineis provided between encoder 5 and radial gate 3.

A circular signal encoder channel 102, including a circular delaycircuit 6, a circular gate 7, a circular oscillator 8 (of standardconstruction) and a circular element signal encoder 9, all connected inseries, is connected to the heading signal output of the radar indicator1 to receive heading signals S,,.

The outputs of encoders 5 and 9 are fed to a mixer 10, the output ofwhich is fed to segment signal composer 11. The remainder of FIG. 1 willbe discussed in detail hereinbelow.

When sweep trigger signal S, is received by the radial signal encoderchannel 101, the trigger signal S, is applied directly to radial delaycircuit 2. Radial delay circuit 2 has a delay corresponding to theradial distance from the origin of the radial sweep to the location onthe radar display at which the desired reference characters shall bestarted in its representation on the radar display. The output of delay2 is applied to a radial gate 3. This enables gate 3 and allows thesignal from delay 2 to pass through gate 3 into radial oscillator 4 toturn radial oscillator 4 on.

The output pulses of radial oscillator 4 are fed to radial elementsignal encoder 5 to drive an internal flip-flop circuit (not shown). Theflip-flop circuit employed in encoder 5 of this invention includes fourstages of flip-flops and performs a cycle of logical AND/OR operationson the output pulse of radial oscillator 4 by means of a diode matrix(not shown) which is also included in the radial element signal encoder5. This results in delivery of a specified number of radial elementsignals encoded against the vertical components of the segmentedalphanumeric characters as shown in FIG. 4 c for later mixing with thecircular element signals which are derived from the circular signalencoder channel as described below.

A rest signal S, is delivered from radial element signal encoder 5 toradial gate 3 when the flip-flops of encoder 5 complete a cycle ofoperation. This turns off radial oscillator 4 until the next sweeptrigger signals S, is applied to radial delay circuit 2, the output ofwhich will cause radial oscillator 4 to be turned on again.

A heading signal S,,, generated by radar indicator 1, is applied tocircular delay circuit 6. Circular delay circuit 6 has a delaycorresponding to the circular distance from the heading to the locationat which a desired reference character shall be started in itsrepresentation on the radar display. The circular signal encoder channel102 operates substantially in the same manner as the radial encoderchannel 101. That is, circular gate 7 is caused to open after the delayperiod of circular delay circuit 6 has expired. This turns on circularoscillator 8. The

output pulses of circular oscillator 8 are then fed to circular elementsignal encoder 9 to drive three stages of internal flipflops (notshown), which perform cycles of logical AND/OR operations on the outputsignal of circular oscillator 8 by means of a dioxide matrix (not shown)which is also included in the circular element signal encoder 9. Thisresults in delivery of a specific number of circular positioning signalsencoded against the horizontal components of the segmented alphanumericcharacters as shown in FIGS. [B and [C for later mixing with the radialsegments signals delivered from the radial signal encoder channel 101.

A reset signal S, is transmitted to circular gate 7 from a characterpositioning means (described hereinbelow) to turn off circularoscillator 8. The reset signal 8, is not generated until circularoscillator'8 has provided the necessary number of circularypositioningsignals for all of the alphanumeric characters to be displayed.

.'The output signals from a radial and circular element signal encoders5 and 9, respectively, are fed in synchronization with each other tomixer '10, wherein the signals are mixed by means of logical AND/ORoperations into successive vertical segment signals which correspond tothe specified vertical components of all alphanumeric characters to bedisplayed [see FIG. 6 (10)].

The segment signal composer 11 receives the output of mixer 10 andcomposes it, through logical AND/OR operations, into a specified numberof pattern signals for the alphanumeric characters to be displayed [seeFIG. 6 (II )1.

The pattern signals thus obtained are applied to an automatic patternsignal :selector 12 or a manual pattern signal selector 14. Theappropriate pattern signals are selected thereby under control of a timesignal generator 13, which supplies clock or timing signals denotingactual time to automatic pattern signal selector 12 through a timememory 18 as well as to a time monitor 17.

The pattern signals-selected by automatic and manual pattern signalselectors 1-2 and 14 are fed to a character-positioning means 15, wheretheir positions are signals are determined. The output signals ofcharacter-positioning means 15 (ie the final pattern signals) are thenapplied to an output controller 16, which combines the final patternsignals with radar video signals 8,. from the radar indicator 1 into acomposite signal S and transmits a composite signal back to the radarindicator I for display. Composite signal S, contains the radarinformation as well as reference character signals.

After character positioning means 15 determines the positions of all ofthe alphanumeric reference characters to be displayed, the reset signalS, is generated by character-positioning means 15 and fedito circulargate 7 to stop the operation of circular oscillator 8.

A more detailed description of the construction and operation of theapparatus of this invention will now be given below with'reference toFIG. 2. Corresponding elements are given the same reference designationswherever possible throughout the drawings.

Referring to FIG. 2, a typical radial delay circuit 2 comprises amonostable multivibrator, which functions to properly position thestarting point of the vertical component of a segmented alaphanumericcharacter on the radial sweep of 'PPI radar indicator 1. That is, themonostable multivibrator is turned on by an input sweep trigger pulse S,shown in FIG. 3 a

and remains on for a predetermined period to time which is determined bythe time constant of the monostable multivibrator. The trailing edge ofthe output of delay circuit 2 opens radial gate 3 as shown in FIGS. 3band 3c. Oscillator 4 is thereby-started. Thus, delay circuit 2 delaysthe start of radial oscillator 4 (Le. the starting point of the verticalcomponent of the segmented alphanumeric characteR) by a delay time whichcorresponds to a distance measured over the radial sweep with respect tothe origin thereof on the display of the PP] indicator of radarindicator 1. A typical composite radar display is shown in'FlG. 9, thestarting point of the alphanumeric display being indicated by A. Avariable resistor and capacitor are provided in the monostablemultivibrator within delay circuit 2 to allow the time constant to bemade variable, thus making the on time" of the multivibrator variabledepending on the working range of the radar. Varying the time constantis accomplished in a manner known in the art. A variable resistorprovides means for making a fine adjustment of the position of thesegmented alphanumeric character in the radial direction.

Radial gate 3 consists of a flipflop of generally well known design. Asdescribed above, the flip-flop circuit is set by the trailing edge ofthe output signal from radial delay circuit 2 [see FIGS. 3b and 3c Theflip-flop in radial'gate 3 remains in the on condition as shown in FIG.3c until reset signal S is applied from radial element signal encoder 5to radial gate 3. It should be clear to those skilled in the art howreset signal 5,, resets the flip-flop in radial gate 3.

The positive voltage level [see FIG. 30 is then applied to radialoscillator 4 to start its oscillation as shown in FIG. 3d. Radialoscillator 4 is stopped when radial gate 3 is turned off by rest signalS This operation can be achieved in various well-known ways by thoseskilled in the art. For example, the radial oscillator 4 may include aninternal switching circuit which turns the oscillator on and off inresponse to the output of gate 3.

Radial oscillator 4 may comprise an astable multivibrator, which enablesadjustment of the height (i.e., the radial width) of the segmentedalphanumeric character displayed on the PP] scope. The switching circuitof radial gate 3 is then connected to the transistors of the astablemultivibrator circuit to turn it on-and-off.

The waveforms of FIGS. 3d and 3e show the output waveform of radialoscillator 4 and the heading signal Sh (to be described hereinafter),respectively.

Radial element signal encoder 5 encodes the output signal of radialoscillator 4 into radial element signals corresponding to the verticalcomponents of the alphanumeric character -to be displayed. Thecharacters to be displayed in this embodiment are divided into five (5)vertical segments to form a mosaic pattern consisting of 5 7=35 mosaicblocks. Accordingly, radial element signal encoder 5 includes a circuitfor encoding the output of radial oscillator 4 into the radial elementsignals required to'properly compose the radial segment signalscorresponding to the five components of the alphanumeric charactersegmented vertically. As shown in FIG. 2, radial encoder 5 includes afour-stage flip-flop circuit 200, the outputs of which are coupled to alogical AND circuit 201 (which comprises a diode matrix and transistorcircuits). The flip-flop circuit 200 divides the frequency of the inputpulses from radial oscillator 4 by 16 at the output of the 4th stageflip-flop (FF 4) by dividing the input frequency by 2 at each of thefour flip-flop stages in flip-flop circuit 200. The frequency divisionis illustrated in FIG. 4 [A], where waveforms 0,2, b, F, 0,5, d and 2show the waveforms appearing at each successive output of the fourstages FFlFF4 of flip-flops 200 and signal S. denotes the output ofradial oscillator 4.

The trailing edge of the waveform dof FIG. 4 [A] is applied to radialgate 3 as the reset signal S This causes radial oscillator 4 to beturned off and all of the flip-flops FFlFF4 in radial element signalencoder 5 remain with their output waveforms in the conditionestablished when the oscillator 4 was turned off.

In the above description, flip-flop circuit 200 includes four stages offlip-flops. However, a three-stage flip-flop circuit could handle theoutput signal S, of radial oscillator 4 for a system using a mosaicpattern with 5X7=35 mosaic blocks. But, when the flip-flop circuitrepeats its ON-and-OFF operation at a high speed, a time interval ofseveral cycles is required before the output frequency of radialoscillator 4 is stabilized. Thus, the radial element signal encoder 5 ofthe present apparatus includes a four-stage flip-flop circuit in orderto allow radial oscillator 4 to provide an output waveform S having 16cycles, the first 8 cycles of which are assigned as stabilizing cyclesand are not used. The next 8 cycles are reserved as the interval duringwhich the logical AND and OR circuits of radial element signal encoder 5are allowed to operate on the output waveforms of radial oscillator 4.

The waveforms (l)(7) shown in FIG. 4 [B] are the seven (7) outputs ofAND circuit 201 of the present embodiment. The design of AND circuits201 to obtain waveforms I )(7) of FIG. 4 [B] from the waveforms of FIG.4 [A] should be apparent to one skilled in the art. Well-known booleanalgebra techniques may be implemented in determining the actual ANDcircuit configuration, which is not shown herein for the sake of clarityso as not to unduly obscure the invention.

FIG. 4 [C] illustrates the digits 0, l ..9, a dash and a decimal point(or period) which are the alphanumeric characters to be displayed by thedescribed apparatus. These characters can be constructed with the 14types of radial segment signals (A) through (N) (also shown in FIG. 4[C]) which correspond to the vertical components of the alphanumericcharacters. The 14 waveforms (A) through (N) of FIG. 4C are obtained bycombining the AND circuit output waveforms (l)(7) of FIG. 4 [B] in ORcircuit 202. The particular design of OR circuit 202 to obtain thewaveforms of FIG. 4C should be apparent to those skilled in the art byusing boolean algebra design techniques.

The present electronic character generating apparatus is designed tohandle 14 types of the radial segment signals to compose an alphanumericcharacter. The number of radial segment signals will naturally bereduced if more simplified patterns are used and will be increased ifmore complex patterns are used.

In the circular signal encoder channel 102, circular delay circuit 6provides the necessary delay for starting circular oscillator 8 in orderthat the horizontal components of an alphanumeric character representedon the PPI display are positioned at the desired position in thecircular direction. Similar to radial delay circuit 2, circular delaycircuit define may include a monostable multivibrator which, whenstarted by a heading signal S operates in the same manner as themonostable multivibrator of radial delay circuit 2. Signal waveforms areas shown in FIG. 3 for the corresponding elements in the circular signalencoder channel 102.

Circular gate 7 is constructed similar to, and operates in the samemanner as, radial gate 3. Circular oscillator 8 may comprise an astablemultivibrator, as in the case of radial oscillator 4, and providesfacilities to define the circular width on a PPI display from theheading line to the starting point of the alphanumeric character to bedisplayed. One of the two transistors in the astable multivibrator ofoscillator 8 has an emitter circuit grounded through the switchingcircuit of circular gate 7 to turn oscillator 8 on when the switchingcircuit of gate 7 is closed. The time constant of oscillator 8 is madevariable to enable fine adjustment of the circular width of thealphanumeric character to be displayed. Oscillator 8 is stopped bysupplying circular gate 7 with reset signal 8,. fromcharacter-positioning means 15, which resets the switching circuit ofgate 7, thereby turning the oscillator 8 off.

Circular element signal encoder 9, similar to radial element signalencoder 5, is composed of a flip-flop circuit 203 having three stagesFFl-FF3 and logical AND and OR circuits 204 and 205, respectively, whichuse diode matrices and transistor circuits. The flip-flop circuit 203 isof the sequential type and performs no high-speed operation. AND circuit204 and OR circuit 205 are not shown in detail for ease of description.

FIG. 5 [A] illustrates output waveforms a, E, b, F, c and E of the threestages of flip-flops FF l-FF3 in circular element signal encoder 9,which are operated by the output waveform S of circular oscillator 8.The signal S is frequency divided by 8 by flip-flops 203 to providewaveform c of FIG. 5 [A] which is sent to character-positioning meanswherein it is used as a reference signal for the number and position ofthe alphanumeric characters to be displayed. The three stages offlip-flop circuit 203 repeat their cycle of operation until a resetsignal S, is sent from character positioning means 15 to circular gate 7after the flip-flops 203 of encoder 9 deliver their final outputsrequired to compose the necessary circular segment signals for all ofthe alphanumeric characters.

FIG. 5 [B] illustrates the output of the AND circuit 204 of encoder 9.FIG. 5 [C] illustrates the outputs of the OR circuit 205 of encoder 9which are the circular positioning signals for an alphanumericcharacter.

In the present system the circular logical OR circuit 205 must provideat least six (6) circular positioning signals. Circular encoder 9 shouldprovide circular segment signals that correspond to an alphanumericcharacter divided into five horizontal segments and an additionalcircular positioning signal is required to provide means forrepresenting a decimal point with an alphanumeric character. Inpractice, circular logical OR circuit 205 provides a total of eightcircular positioning signals as shown in FIG. 5 [C], of which theadditional two positioning signals are intended to simplify the logicaloperation of the radial segment signals assigned to the alphanumericcharacters, 3, 4, 5, 6 and etc. which have the common three verticalcomponents in their pattern (see FIG. 4 [C]).

The coded radial and circular element signal mixer 10 consists of 22sets of mixing circuits, each set including a logical AND and aninverter circuit. Only three AND circuits 2022 and associated invertercircuits 2325 are shown for ease of description. Mixer [0 receives theoutput signals of both the radial and circular signal encoder channels101 and 102, respectively, and mixes them to derive segment signals. Thecoded radial element signals define the radial position of the segmentsignals and the circular positioning signals define the duration of thesignal.

Segment signal composer 11 comprises a diode matrix 206 for performing alogical AND operation on the outputs of mixer 10. The matrix outputs arecoupled to inverters 207 which function as logical OR circuits. ComposerlI composes the segment signals supplied form signal mixer 10 into thealphanumeric character pattern signals, as described below.

In summary, the coded radial and circular element signal mixer 10 andthe segment signal composer 11 function to convert the outputs of theradial and circular signal encoder channels into an alphanumericcharacter pattern signal. This will be explained below with reference toFIG. 6, which illustrates converting the coded radial and circularelement signals into a specific alphanumeric character pattern signalfor representation of a digit three (3).

Coded radial element signal (B) (see FIG. 4 [C]) from radial elementsignal encoder 5 and coded circular element signals (see FIG. 5 [C fromcircular element signal encoder 9 are converted by signal mixer 10 intoa segment signal (58). Similarly, radial element signals (D) and (E) andcircular element signals and are converted into segment signals (6D) and(1E), respectively, in mixer 10. These segments signals (58), (6D) and(1E) are then applied to segment signal composer II, where said segmentsignals are converted by means of a logical OR operation in composer 11into the alphanumeric character pattern signal for representation of amosaic pattern digit three (3). The particular design of mixer 10 andcomposer 11 to obtain the signals of FIG. 6 should be apparent.

Automatic pattern signal selector 12, consisting of logical AND and ORcircuits 208, 209, respectively (shown in more detail in FIG. 7),selects the required alphanumeric character pattern signal among theoutput signals of segment signal composer 11 under control of the clocksignals fed from time signal generator 13 and sends them tocharacter-positioning means 15. The selection process is described belowwith reference to FIG. 7.

The time signal generator 13 may comprise for example, a crystal clockwith fundamental frequency of kHz. The fundamental frequency isfrequency divided within generator 13 to produce the time signalscomprising six types of clock signal, i.e. the second," lO-second,minute," 10- minute, hour," and 10-hour" clock signals, which are feddirectly, or, in this embodiment, via time memory 13 to the automaticpattern signal selector E2.

The time signals from time signal generator 13 are also fed to a timemonitor 17, where they are displaced by a digital indicator to monitorthe digits indicating the actual time.

Time memory 18, as shown in FIG. 2, is mainly composed of flip-flopcircuits 26-28, a gate circuit 29 comprised of a plurality of AND gates,an inverter circuit 30, a monostable multivibrator 31 and anemitter-follower amplifier circuit 32. The output of monostablemultivibrator 31 is fed by means of the emitter-follower amplifiercircuit 32 to the gate 29. A pulse similar to the waveform of FIG. 3b isapplied from the circular delay circuit 6 in the circular signal encoderchannel to the monostable multivibrator 31 of the time memory 18 totrigger the multivibrator on the leading edge thereof.

In the present embodiment, time signal generator 13 delivers a total of45 output pulses, which include 10 second" pulses, 6 10-second" pulses,10 minute" pulses, 6 10-minute" pulses, 10 hour" pulses and 3 10-hour"pulses. These pulses are required for digital representation of theactual time.

Accordingly, 45 connecting lines are required between the time signalgenerator 13 and the automatic pattern signal selector 12. Therefore,time memory l8 must also have 45 input terminals and '45 outputterminals.

The time memory 18 memorizes the circular position of an alphanumericcharacter pattern signal starting to appear on a radar indicator displayand the time thereof (the time for start of an alphanumeric characterpattern signal representation in this apparatus).

A trigger pulse [shown in FIG. 3b 1 is applied from the circular delaycircuit-.6 to time memory 18 and resets the flipflops 26-28 in timememory 18 with the rising edge thereof to erase the previous memories.Flip-flops 2628, after the falling edge of the trigger pulse of FIG. 3bstart the memory operation and later memorize second, 10-second,"minute," 10-minute, hour" and Ill-hour time pulses. These timepulses'are supplied from time signal generator 113 through the gates 29of time memory 18 to flip-flops 26-28 when the gates 29 are enabled byan extremely short pulse generated by the monostable multivibrator 3iwhich was started with the falling edge of the trigger pulse applied tothe time memory 18. Under normal conditions, the gate circuits 29 intime memory 18 are in the nonconducting condition to isolate the flipflops 26-28 from the time signals incoming from time signal generatorl3. When triggered, the gate circuits conduct and allow the time signalsto pass through them to the flip-flops 2628. Thus, a flip-flop 26-28 ischanged into its inverse condition by a time signal only when .121 pulseof several as is applied to its associated gate in gate circuit 29 frommonostable multivibrator 31. The flip-flops 26- -28 remain in thatcondition for memorizing the time signal, until it receives a resetsignal via inverter 30.

The purpose of time memory H8 is to prevent the cathode ray tube on thePPI indicator from giving an erroneous time indication during thechanging of a time reference display.

Suppose now that the present apparatus is going to display an actualtime reference of 21 oclock, 12 minutes, 39 seconds. PPI indicator 1will start to represent said time reference on its PPl scope in thecircular clockwise direction with its radial sweep which, rotating insynchronization with the radar antenna, completes one turn in 0.3 to 0.5seconds. If the actual time becomes 21 oclock, 12 minutes, 40 secondsduring the later circular sweep of the radial sweep, then there willexist a problem in that the actual time will be erroneously indicatedvirtue 21 oclock, 12 minutes, 49 seconds, instead of 40 seconds. is dueto the image of the number 9 remaining on the PP! scope by virtue of theimage persistance of the PPI scope. Time memory 18 is provided toeliminate this malfunction by allowing the time to change only at thebeginning, and not during, the sweep.

Time signal generator 113 delivers the second time signals 0-9 and theIO-second" time signals 0-5, which are shown in FIG. 7, to automaticpattern signal selector 12. In FIG. 7, the time memory 18 signals arenot shown for the sake ofclarity. The time signal generator 13 repeatsdelivery of a second pulse to the second" signal lines 0 t0 9 of FIG. 7which correspond respectively to digits 0-9 in order at intervals of onesecond and also a 10-second pulse to the 10- second" signal lines l to 5in order at intervals of 10 seconds. Provision is made, as mentionedpreviously, to advance the delivery of the lO-second pulse by one secondat the moment when the second" pulse is shifted from the second" signalline 9 to the second" signal line 0 in time signal generator 13.

Time signal generator 13 also delivers the minute, 10- minute," hour and10-hour" pulses to automatic pattern signal selector 12 in a similarmanner as described above with respect to FIG. 7. Therefore, thefunction of time signal generator 13 concerning delivery of the minute,10- minute," hour and IO-hour" pulses is not described in detail hereinfor the sake of clarity.

The automatic pattern signal selector l2 selects the necessaryalphanumeric character pattern signal among the outputs from the segmentsignal composer 11 in accordance with the time signals delivered fromsaid time signal generator 13. The simplified pattern signal selector ispartially shown in FIG. 7 by way of example only, and includes AND gates33-41 and OR gates 42 and 43 to make the appropriate selections ofsignals. It should be clear that selector 12 may take other forms,depending upon system requirements. Now, suppose that a time signal of25" is delivered from the time signal generator 13 to the automaticpattern signal selector 12. This corresponds to a condition where thesecond pulse is applied to the second signal line 5 and the IO-secondpulse to the l0-second signal line 2, with no pulses being applied toother signal lines. The gate circuits 36 and 40 in the automatic patternsignal 12 are then enabled, thereby allowing the alphanumeric characterpattern signals for mosaic pattern 5 and .2 rom segment signal composer11 to pass through the gates 36 and 40. Thus, as shown in FIG. 7, in theuse of second and IO-seond alphanumeric character pattern signals 5 and2, respectively, the numeral character pattern signals from segmentsignal composer 11 are selected by the AND gates of selector 112 as thesignals for the digits in the second" and l0-second" positions. Thesesignals are illustrated in FIG. 7 on the AND gate output leads withinselector 12. These signals are passed through OR gates 42 and 43 wherethey are composed into the signals illustrated in FIG. 7 as the selectoroutputs and are then fed to the character-positioning means 115.

The above description is given for the case where the time signalgenerator 13 and the automatic pattern signal selector to 112 areconnected together without the time memory 18. These functions are notsubstantially changed when the time signal generator 113 and automaticpattern signal selector 12 are operated with the time memory 18 insertedbetween them.

Thus, logical OR circuits (209 of FIG. 2; 42, 43 of- FIG. 7) in selectorl2 sequentially deliver the second and 10- second signals (shown in FIG.7) on the two output lines 44 and 45, respectively, of selector 12 insuch manner that the second and lll-seond" pulses corresponding todigits 0-9 and O-5 are successively shifted at every second and 10seconds, respectively, before they are a plied to the character;

positioning means 115. Character-positioning means 15 is provided tocorrectly position the characters on the PPI display.

The manual pattern signal selector l4 consists of a plurality ofinverters 2110 and rotary switches Zll, each switch being associatedwith a respective inverter. Selector 14 selects the necessaryalphanumeric character pattern signal among the outputs from the segmentsignal composer 111 as the automatic pattern signal selector 12 does,but in accordance with the alphanumeric character patterns which arepreset on the plupresent embodiment. there are 6 inverters and 6 rotaryswitches. one for each numeric character. Other configurations can beused.

The above mentioned plurality of inverters 210 and rotary switches 211.provide for selection of the semitixed alphanumeric character patternsignals; for example, those corresponding to the digits expressing ayear, month and day. The necessary alphanumeric character patternsignals are selected in accordance with the setting of the rotaryswitches and re delivered through the switches 211 to thecharacter-positioning means 15. Thus, the alphanumeric character patternsignals selected by and delivered from the automatic and manual patternsignal selectors 12 and 14, respectively, are applied to thecharacter-positioning means 15 wherein they are ANDed with positioningpulses (which will be described later) to correctly position thecharacters on the PPI scope.

The character positioning means 15 is composed of four (4) stages ofsequential-type flip-flops 212 and logical AND and OR circuits 213 and214, respectively. The number of the stages of flip-flops in thesequentialtype flip-flop circuit 212 is determined by the number ofalphanumeric characters to be displayed. In the present case, fourflip-flop stages enable the display of 15 alphanumeric characters,inclusive of the spaces between the characters. One character isdisplayed during each count of the flip-flop circuit 212. The 16th countis used for resetting the circuit.

To start the flip-flops 212, the pulse Eshown in FIG. [A] and in FIG. 8[A] is applied from the circular element signal encoder 9 to theflip-flops 212. This causes, as shown in FIG. 8 [A], the flip-flops 212to deliver output waveforms d and (T at the 1st stage FFl and waveformse and E, f and Tand g and g at stages FF2, FF3 and FF4, respectively. Inother words, flipflops 212 provide one pair of its output pulses g and gat stage FF4 after they receive 16 F pulses. The last output pulse E isfed back as reset signal 5, to the circular gate 7 and reset theflipflops in the circular gate 7 with its trailing edge. This stops theoperation of circular oscillator 8 after delivery of the required numberof output signals for alphanumeric characters, inclusive of the spacebetween the characters.

The output waveforms d, (T, g and ,1} obtained from the four stages offlip-flops 212 are applied to the logical AND circuit 213, whichcomprises a diode matrix of the characterpositioning means 15. Theoutputs of selectors 12 and 14 are applied to AND circuit 213 ofpositioning means 15. AND circuit 213 operates on these signals togenerate the 13 types of positioning pulses A through A shown in FIG. 8[B].with a space being provided between pulses A. A and A, A The signalsA A are then applied to the logical OR circuit 214 of characterpositioning means 15.

As stated above, logical AND circuit 213 performs a logical ANDoperation on the alphanumeric character pattern signals from theautomatic and manual pattern signal selectors 12 and 14, respectively,with the positioning signals from flip-flops 212 to generate theabove-mentioned 13 types of positioning pulses, shown in FIG. 8 [B].That is, appropriate pattern signals from selectors are combined incoincidence with their corresponding positioning pulses. The combinedsignals are further combined in OR circuit 214 to form a pulse train,which is delivered to the output controller 16.

The output controller 16 consists of a mixer circuit 215 and anemitter-follower amplifier 216, and provides the necessary impedancematching between the radar video signal S received from the PPIindicator 1 and the output pulse train supplied from thecharacter-positioning means 15. Mixer 215 mixes these signals into acomposite signal S which, after being adjusted to provide the properintensity on the PPI scope (by means not shown), is delivered to the PPIindicator 1. Composite signal S contains both signals representing theradar information and signals representing the alphanumeric charactersto be displayed simultaneously with the radar dislay. p The abovedescription of the present invention is directed mainly to a system forrepresentation of an electronic alphanumeric time reference on a PPIscope of a radar indicator. The apparatus is of course capable ofrepresenting references other than time references and is capable ofrepresenting any pattern other than the alphanumeric characters withinthe spirit of the invention.

This invention further allows its time reference signals to be recordedas the polar coordinate information signals together with the videosignals for a radar display on a magnetic tape. When later reproduced,the time reference signals on the recorded radar display provide meansfor an effective identification and verification of the validity of thereproduced radar display.

It is pointed out that the radar indicator 1 with which the systemaccording to the preset invention is used is well known in the art. Theradar indicator 1 generates the heading and trigger signals in awell-known manner.

It is further pointed out that he logical AND and OR gating circuitrygenerally shown in the drawings as elements 201, 202, 204, etc., areshown merely by way of example. The internal connections within thegating circuitry is capable of being designed by one ordinarily skilledin the art in view of the detailed description set forth above taken inconjunction with the various illustrations of the waveforms appearing atthe inputs and outputs of the various devices. Depending upon the typesof characters desired, the AND and OR gating circuitry may take variousdifferent forms, as is well known in the art.

We claim:

1. Electronic character-generating system for a radar system generatingfirst and second reference signals, comprising:

a radial signal encoder channel responsive to said first referencesignal for generating coded radial element signals;

a circular signal encoder channel responsive to said second referencesignal for generating coded circular element signals;

means coupled to said radial and circular signal encoder channels forgenerating a plurality of pattern signals representing a plurality ofcharacters from said coded circular element signals and coded radialelement signals;

a pattern signal selector for selecting predetermined pattern signalsfrom said plurality of pattern signals;

character-positioning means for combining character position informationsignals with said selected pattern signals to position said selectedpattern signals at a desired position on the display of said radarsystem; and

means for mixing the output signals from said characterpositioning meanswith radar video signals from said radar system to form compositesignals, said composite signals being transmitted to said radar systemand displayed on the radar display thereof.

2. System according to claim 1, wherein said first and second referencesignals are trigger and heading signals, respectively.

3. System according to claim 1, wherein said pattern signal generatingmeans includes:

means for deriving segment signals from said coded circular elementsignals and coded radial element signals;

and means for comprising said segment signals into said plurality ofpattern signals representing a plurality of characters.

4. System according to claim 1, wherein said radial signal encoderchannel includes:

a radial delay circuit coupled to receive said first reference signalfrom said radar system and delaying said first reference signal for afirst predetermined period of time;

a radial oscillator responsive to the output of said radial delaycircuit for generating a plurality of radial element signals;

a radial element encoder for encoding said radial element signals intocoded radial element signals; and

means responsive to an output from said radial element encoder to turnoff said radial oscillator after a predetermined number of radialelement signals have been generated.

5. System according to claim 4, wherein said means for turning off saidradial oscillator includes a gate circuit coupled between said radialdelay circuit and said radial oscillator. said gate circuit beingresponsive to said radial element encoder output to cause said radialoscillator to be turned off after generation of said predeterminednumber of radial element signals.

6. System according to claim 1, wherein said circular signal encoderchannel includes:

a circular delay circuit coupled to receive said second reference signalfrom said radar system and delaying said second reference signal for asecond predetermined period of time;

a circular oscillator responsive to the outputof said circular delaycircuit for generating a plurality of circular element signals; and

a circular element encoder for encoding said circular element signalsinto coded circular element signals.

7. System according to claim 6, further comprising a second gatingcircuit coupled between said circular delay circuit and said circularoscillator.

8. System according to claim 7, wherein said radial signal encoderchannel includes:

a radial delay circuit coupled to receive said first reference signalfrom said radar system and delaying said first reference signal for afirst predetermined period of time;

a radial oscillator responsive to the output of said radial delaycircuit for generating a plurality of radial element signals;

a radial element encoder for encoding said radial element signals intocoded radial element signals; and

means responsive to an output from said radial element encoder to turnofi said radial oscillator after a predetermined number of radialelement signals have been generated.

9. System according to claim 8, further comprising:

a timing circuit; and

means feeding an output of said circular delay circuit to said timingcircuit as a trigger signal.

System according to claim 3, further comprising means coupling an outputof said circular element signal encoder to said character positioningmeans as a trigger signal.

ill. System according to claim 8, further comprising means coupling asignal from said character-positioning means to said second gatingcircuit to cause said second gating circuit to turn off said circularoscillator after signals representing a predetermined number ofcharacters have been generated.

l2. System according to claim 3, wherein said deriving means includes asignal mixer for logically combining said coded circular and codedradial element signals into said segment signals.

13. System according to claim l2, wherein said composing means includesmeans for logically combining said segment signals into pattern signalsrepresenting predetermined characters.

14-. System according to claim 1, further comprising a source oftimingsignals coupled to said pattern signal selector, said patternsignal selector selecting predetermined pattern signals in accordancewith the outputs from said timing means.

15. System according to claim 14, wherein said timing means includes:

a time signal generator generating a plurality of types of timingsignals; and

means coupling said plurality of types of timing signals to said patternsignal selector.

llt). System according to claim l5, further comprising a time memorycoupling said plurality of types of time signals to said pattern signalselector, said time memory including means for memorizing said pluralitof types of time signals.

ll7. System according 0 claim 16, further comprising means coupling atrigger signal from said circular delay circuit to said time memory toenable said time memory.

118. System according to claim ll, wherein said pattern signal selectorincludes a manual pattern signal selector having a plurality of switchesfor preselecting predetermined pattern signals.

39. System according to claim 14, further comprising means coupling :heoutput of said timing means to said characterpositioning means, saidcharacter-positioning means logically combining said pattern signalswith said time signals into a pulse train signal which representspredetermined characters.

1. Electronic character-generating system for a radar system generatingfirst and second reference signals, comprising: a radial signal encoderchannel responsive to said first reference signal for generating codedradial element signals; a circular signal encoder channel responsive tosaid second reference signal for generating coded circular elementsignals; means coupled to said radial and circular signal encoderchannels for generating a plurality of pattern signals representing aplurality of characters from said coded circular element signals andcoded radial element signals; a pattern signal selector for selectingpredetermined pattern signals from said plurality of pattern signals;character-positioning means for combining character position informationsignals with said selected pattern signals to position said selectedpattern signals at a desired position on the display of said radarsystem; and means for mixing the output signals from saidcharacterpositioning means with radar video signals from said radarsystem to form composite signals, said composite signals beingtransmitted to said radar system and displayed on the radar displaythereof.
 2. System according to claim 1, wherein said first and secondreference signals are trigger and heading signals, respectively. 3.System according to claim 1, wherein said pattern signal generatingmeans includes: means for deriving segment signals from said codedcircular element signals and coded radial element signals; and meanS forcomprising said segment signals into said plurality of pattern signalsrepresenting a plurality of characters.
 4. System according to claim 1,wherein said radial signal encoder channel includes: a radial delaycircuit coupled to receive said first reference signal from said radarsystem and delaying said first reference signal for a firstpredetermined period of time; a radial oscillator responsive to theoutput of said radial delay circuit for generating a plurality of radialelement signals; a radial element encoder for encoding said radialelement signals into coded radial element signals; and means responsiveto an output from said radial element encoder to turn off said radialoscillator after a predetermined number of radial element signals havebeen generated.
 5. System according to claim 4, wherein said means forturning off said radial oscillator includes a gate circuit coupledbetween said radial delay circuit and said radial oscillator, said gatecircuit being responsive to said radial element encoder output to causesaid radial oscillator to be turned off after generation of saidpredetermined number of radial element signals.
 6. System according toclaim 1, wherein said circular signal encoder channel includes: acircular delay circuit coupled to receive said second reference signalfrom said radar system and delaying said second reference signal for asecond predetermined period of time; a circular oscillator responsive tothe output of said circular delay circuit for generating a plurality ofcircular element signals; and a circular element encoder for encodingsaid circular element signals into coded circular element signals. 7.System according to claim 6, further comprising a second gating circuitcoupled between said circular delay circuit and said circularoscillator.
 8. System according to claim 7, wherein said radial signalencoder channel includes: a radial delay circuit coupled to receive saidfirst reference signal from said radar system and delaying said firstreference signal for a first predetermined period of time; a radialoscillator responsive to the output of said radial delay circuit forgenerating a plurality of radial element signals; a radial elementencoder for encoding said radial element signals into coded radialelement signals; and means responsive to an output from said radialelement encoder to turn off said radial oscillator after a predeterminednumber of radial element signals have been generated.
 9. Systemaccording to claim 8, further comprising: a timing circuit; and meansfeeding an output of said circular delay circuit to said timing circuitas a trigger signal.
 10. System according to claim 8, further comprisingmeans coupling an output of said circular element signal encoder to saidcharacter positioning means as a trigger signal.
 11. System according toclaim 8, further comprising means coupling a signal from saidcharacter-positioning means to said second gating circuit to cause saidsecond gating circuit to turn off said circular oscillator after signalsrepresenting a predetermined number of characters have been generated.12. System according to claim 3, wherein said deriving means includes asignal mixer for logically combining said coded circular and codedradial element signals into said segment signals.
 13. System accordingto claim 12, wherein said composing means includes means for logicallycombining said segment signals into pattern signals representingpredetermined characters.
 14. System according to claim 1, furthercomprising a source of timing signals coupled to said pattern signalselector, said pattern signal selector selecting predetermined patternsignals in accordance with the outputs from said timing means. 15.System according to claim 14, wherein said timing means includes: a timesignal generator generating a plurality of types of timing signals; andmeans coupling said plurality Of types of timing signals to said patternsignal selector.
 16. System according to claim 15, further comprising atime memory coupling said plurality of types of time signals to saidpattern signal selector, said time memory including means for memorizingsaid plurality of types of time signals.
 17. System according to claim16, further comprising means coupling a trigger signal from saidcircular delay circuit to said time memory to enable said time memory.18. System according to claim 1, wherein said pattern signal selectorincludes a manual pattern signal selector having a plurality of switchesfor preselecting predetermined pattern signals.
 19. System according toclaim 14, further comprising means coupling the output of said timingmeans to said character-positioning means, said character-positioningmeans logically combining said pattern signals with said time signalsinto a pulse train signal which represents predetermined characters.